JP6906614B2 - Systems and methods for defective material classification - Google Patents

Description

The present disclosure relates generally to defective material classification, and more specifically to classifying defective materials based on defect scattering properties.

Cross-reference to related applications This application is based on Article 119 (e) of the US Patent Act and is entitled "DEFECT MATERIAL CLASSIFICATION" filed on January 5, 2017 by the inventor Guoheng Zhao, J. Mol. K. Claiming priority in US Provisional Patent Application No. 62 / 442,838 in the name of Leong and Mike Kirk, the provisional patent application is incorporated herein by reference in its entirety.

The semiconductor manufacturing environment is typically highly controlled to control wafer contamination with foreign matter that can interfere with the machining process or degrade the performance of the machined device. Inspection systems are commonly used, but not limited to, as screening and workarounds to locate defects such as foreign particles on a substrate. For example, untreated wafers may be selected from only suitable wafers or screened prior to manufacture to identify defective sites on the wafer for manufacture. In addition, it may be desirable to classify the material composition of the identified defects in order to determine the appropriate cleaning or avoidance steps throughout the processing process.

U.S. Patent Application Publication No. 2016/0377548

However, the reduced size of machined features drives the need to detect and classify ever-shrinking defects on the substrate, which can pose challenges to the sensitivity and throughput of inspection systems. Therefore, there is an important need to develop systems and methods for detecting small particles in wafer inspection systems.

The inspection system is disclosed by one or more exemplary embodiments of the present disclosure. In one exemplary embodiment, the system includes one source of illumination for producing an illumination beam. In another exemplary embodiment, the system includes one or more focusing elements for directing the illumination beam towards the sample. In another exemplary embodiment, the system comprises a detector. In another exemplary embodiment, the system comprises one or more collecting elements configured to direct the radiation emitted from the sample towards the detector. In another exemplary embodiment, the radiation emitted by the sample includes radiation specularly reflected by the sample and radiation scattered by the sample. In another exemplary embodiment, the system detects for imaging a sample in two or more detection modes so that the detector produces two or more collection signals based on the two or more detection modes. Includes mode controller. In another exemplary embodiment, the system comprises a controller. In another exemplary embodiment, the controller determines one or more defect scattering properties associated with radiation scattered by one or more defects on the sample based on two or more collected signals. In another exemplary embodiment, one or more defect scattering properties include at least one of scattering phase, scattering intensity or defect absorption. In another exemplary embodiment, the controller classifies one or more defects based on one or more defect scattering properties according to a set of predetermined defect classifications.

The inspection system is disclosed by one or more exemplary embodiments of the present disclosure. In one exemplary embodiment, the system comprises an illumination source that produces an illumination beam. In another exemplary embodiment, the system comprises one or more focusing elements configured to direct the illumination beam towards the sample. In another exemplary embodiment, the system comprises a detector. In another exemplary embodiment, the system comprises one or more collecting elements that direct the radiation emitted from the sample towards the detector. In another exemplary embodiment, the radiation emitted by the sample includes radiation specularly reflected by the sample and radiation scattered by the sample. In another exemplary embodiment, the system was selected with two or more different choices between the radiation specularly reflected by the sample and the radiation scattered by the sample so that the detector produces two or more collected signals. Includes a phase controller that introduces a phase offset. In another exemplary embodiment, the system comprises a controller. In another exemplary embodiment, the controller determines one or more scattering phase values introduced into the illumination beam scattered by one or more defects on the sample based on the two or more acquired signals. In another exemplary embodiment, the controller classifies one or more defects based on one or more scattering phase values according to a set of predetermined defect classifications.

The inspection system is disclosed by one or more exemplary embodiments of the present disclosure. In one exemplary embodiment, the system includes an illumination source that produces an illumination beam. In another exemplary embodiment, the system includes one or more focusing elements that direct the illumination beam at the sample. In another exemplary embodiment, the system comprises a detector. In another exemplary embodiment, the system comprises one or more collecting elements that direct the radiation emitted from the sample towards the detector. In another exemplary embodiment, the radiation emitted by the sample includes radiation specularly reflected by the sample and radiation scattered by the sample. In another exemplary embodiment, the system produces a dry image on the detector as a dry collection signal based on the radiation emitted from the sample and based on the radiation emitted from the sample contained within the immersion device. Includes a detection mode controller configured to sequentially generate a water immersion image as an immersion collection signal on the detector. In another exemplary embodiment, the system comprises a controller. In another exemplary embodiment, the controller compares the dry collection signal with the immersion collection signal to detect one or more defects on the sample. In another exemplary embodiment, the controller classifies one or more defects according to a set of predetermined defect classifications based on a comparison of the dry and immersion collection signals.

One or more exemplary embodiments of the present disclosure disclose defect classification methods. In one exemplary embodiment, the method comprises illuminating the sample with an illumination beam. In another exemplary embodiment, the method comprises collecting the illumination emitted from the sample using two or more detection modes to generate two or more collection signals. In another exemplary embodiment, the radiation emitted from the sample includes radiation specularly reflected from the sample and radiation scattered from the sample. In another exemplary embodiment, the method comprises determining one or more defect scattering properties associated with radiation emanating from one or more defects on a sample based on two or more collected signals. .. In another exemplary embodiment, one or more defect scattering properties include at least one of scattering phase, scattering intensity or defect absorption. In another exemplary embodiment, the method comprises classifying one or more defects based on one or more defect scattering properties according to a selected set of predetermined defect classifications.

It should be understood that both the general description above and the detailed description below are representative and descriptive and do not necessarily limit the invention as described in the claims. The accompanying drawings, which are incorporated herein by reference and constitute a portion thereof, serve to illustrate embodiments of the present invention and explain the principles of the present invention together with general description.

The advantages of this disclosure will be better understood by those skilled in the art by reference to the accompanying figures.

FIG. 6 is a conceptual diagram of an inspection system configured for illumination of a sample and collection of radiation emitted from the sample with a common objective according to one or more embodiments of the present invention. FIG. 5 is a conceptual diagram of an inspection system including four stationary phase plates according to one or more embodiments of the present invention. FIG. 5 is a conceptual diagram of an inspection system for phase shift phase contrast imaging in which the relative phases of specular and scattered radiation from a sample are controlled by a phase plate according to one or more embodiments of the present invention. FIG. 6 is a conceptual diagram of an illumination beam with an annular profile for phase shift phase contrast imaging according to one or more embodiments of the present invention. FIG. 6 is a conceptual diagram of an inspection system for phase shift phase contrast imaging using coherent illumination according to one or more embodiments of the present invention. It is a simplified schematic diagram of the polarizer mask according to one or more embodiments of the present invention. FIG. 5 is a plot of a complex relative permittivity as a function of the wavelength of a typical material used in semiconductor manufacturing, which may be associated with defects, according to one or more embodiments of the present invention. FIG. 6 is a plot of an absorption cross section as a function of the scattering cross section of particles at a wavelength of 266 nm for different grain diameters based on a Rayleigh scattering model according to one or more embodiments of the present disclosure. FIG. 6 is a plot of scattering phases as a function of wavelengths of various materials, based on a Rayleigh scattering model, according to one or more embodiments of the present disclosure. FIG. 5 is a plot of an FDTD simulation of a phase shift phase contrast signal of 20 nm particles of various common foreign objects at a wavelength of 266 nm as a function of phase offset according to one or more embodiments of the present disclosure. FIG. 5 is a plot of measured phase shift phase contrast signals of 100 nm particles of various common foreign objects as a function of sample focal position according to one or more embodiments of the present disclosure. FIG. 6 is a plot comprising an FDTD simulation of 100 nm particles of gold, silicon dioxide and copper under the same conditions as the data shown in FIG. 6 according to one or more embodiments of the present disclosure. FIG. 5 is a flow chart showing steps performed by a method of detecting and classifying defects based on defect scattering characteristics according to one or more embodiments of the present disclosure.

Hereinafter, the disclosure contents described in the attached drawings will be referred to in detail. The present disclosure is specifically illustrated and described with respect to a particular embodiment and its particular features. The embodiments described herein are considered exemplary rather than limited. It will be readily appreciated by those skilled in the art that various changes and modifications can be made in their form and details without departing from the spirit and scope of the present disclosure.

1A-8 are generally referred to. The embodiments of the present disclosure cover systems and methods for defect detection and classification based on defect scattering properties. In general, defects can exhibit different particle scattering properties than the surrounding substrate. Thus, defects can be classified based on, but not limited to, differences in scattering characteristics, including scattering phase, scattering ability or defect absorption. An additional embodiment is intended to measure defect scattering properties by analyzing the interference between the radiation reflected by the sample and the radiation scattered by the sample. An additional embodiment is intended to measure defect scattering properties by imaging the sample in a series of detection modes intended to distinguish particle scattering properties associated with different material types. For example, defect scattering properties can be measured using phase shift phase contrast imaging. As another example, a sample brightfield image can provide defect absorption data, whereas a sample darkfield image can provide particle scattering data. Thereby, comparison of the bright-field and dark-field images of the sample may provide particle scattering properties for the detection and classification of defects on the sample. By additional example, the scattering cross sections of different material types differ based on the immersion medium surrounding the sample so that the comparison of sample images is taken with different immersion media (eg, water immersion, oil immersion, etc.). obtain. Therefore, such measurements can reveal particle scattering properties for defect detection and classification.

The promotion to processing smaller semiconductor devices will lead to an increase in demand for substrate uniformity and cleanliness. The tolerance that the semiconductor wafer must be defect-free is commensurate with the size of the machined equipment. Inspection systems are typically used in semiconductor manufacturing environments to detect and / or classify foreign and / or structural defects such as, but not limited to, point or line defects. In a general sense, the inspection system may detect any type of defect on the sample at any time during the manufacturing process. For example, the inspection system may characterize the untreated wafer prior to manufacture and select only the appropriate wafers for manufacture or identify defective sites on the wafer. In addition, it may be desirable to classify the material composition of the identified defects so that appropriate cleaning or avoidance steps can be taken during the entire processing process. The embodiments of the present disclosure cover systems and methods for simultaneous detection and classification of the material composition of defects on a sample.

As used throughout this disclosure, the term "sample" generally refers to a substrate made of a semiconductor or non-semiconductor material (eg, wafer, etc.). For example, semiconductor or non-semiconductor materials can include, but are not limited to, single crystal silicon, gallium arsenide and indium phosphide. In addition, the term samples and wafers should be construed as compatible in this disclosure.

It is recognized herein that defect classification can have challenges in terms of sensitivity to small particles as well as throughput. For example, Energy Dispersive X-ray Analysis (EDX) can provide sensitive defect material analysis capabilities for some materials, but can have improperly slow throughput, inorganic compounds or organic particles. May not be appropriate for. The use of EDX in scanning electron microscopy is generally described in US Pat. No. 6,407,386, which is incorporated herein by reference in its entirety. Alternatively, Nomalski interference spectroscopy may be used to provide the index of refraction of the particles based on the attenuation and phase change measurements of the focused laser beam specularly reflected by the sample, but with low specular small particles. Provides a low signal. The use of Nomalski interference spectroscopy for refractive index determination is incorporated herein by reference in its entirety. A. Taubenblatt & J.M. S. It is generally described in Batchelder's Applied Optics 30 (33), 4972, (1991).

Without limitation, it may be desirable to utilize scattered light to detect and / or classify defects, especially for small particles. However, such methods may also have issues with sensitivity or lighting requirements. For example, Raman spectroscopy can provide material classification based on the excitation of vibration modes that represent a material-dependent shift (eg, Raman shift) between the wavelengths of incident illumination and inelastically scattered illumination. However, the signal intensity of Raman spectroscopy is proportional to the degree to which the excited vibration mode affects the polarizability of the material so that pure metals cannot be detected without an oxidation step. Moreover, Raman scattering is relatively weak (eg, relative to elastic Rayleigh scattering), as long signal integration times limit the usefulness of techniques for small particles. Raman spectroscopy is generally described in Andres Cantanaro, Procedia Material Science 9, 113-122, (2015), which is incorporated herein by reference in its entirety. As another example, scattering spectroscopy can provide material properties as a function of wavelength from the scattering power. ^{Particle scattering is inversely proportional to wavelength (as λ -4} ), although a large range of wavelength differences is typically required to extract material properties. Therefore, sensitivity to smaller particles is limited by the longest wavelength of the illumination source.

Embodiments of the present disclosure detect defects based on defect scattering characteristics such as, but not limited to, the scattering phase associated with the illumination scattered by the defect, the intensity of the illumination scattered by the defect, or the absorption of the illumination by the defect. The target is to classify. A further embodiment of the present disclosure is intended to measure defect scattering properties using a narrowband illumination source. As used herein, the use of narrowband illumination sources can facilitate both sensitive defect detection and classification by efficient scattering of short wavelength illumination and efficient utilization of spectral energy from the illumination source. Be recognized. Accordingly, embodiments of the present disclosure may facilitate sensitive detection and classification of defects, including small particles, at high throughput suitable for use in a processing environment, without limitation.

1A-1F include a conceptual diagram of an inspection system 100 for detecting and / or classifying defects based on defect scattering according to one or more embodiments of the present disclosure.

FIG. 1A is a conceptual diagram of an inspection system 100 configured for illumination of sample 102 and collection of radiation emitted from sample 102 with a common objective lens 104 according to one or more embodiments of the present disclosure.

In one embodiment, the inspection system 100 includes an illumination source 106 configured to generate at least one illumination beam 108. The illumination beam 108 is one or more selected of light including, but not limited to, vacuum ultraviolet (VUV) radiation, deep ultraviolet (DUV) radiation, ultraviolet (UV) radiation, visible radiation or infrared (IR) radiation. May include wavelength. The illumination source 106 may include, but is not limited to, a monochromatic light source (eg, a laser), a multicolor light source having a spectrum containing two or more distinct wavelengths, a broadband light source, or a wavelength sweep light source. Further, the illumination source 106 is not essential, but is a white light source (eg, a broadband light source having a spectrum including a visible wavelength), a laser source, a free-form illumination source, a unipolar illumination source, a multipolar illumination source, an arc lamp, and none. It may be formed from an electrode or a laser maintenance plasma (LSP) source.

In another embodiment, the spectrum of the illumination beam 108 is adjustable. In this regard, the wavelength of the radiation of the illumination beam 108 may be matched to any selected wavelength of radiation (eg UV radiation, visible radiation, infrared radiation, etc.).

In another embodiment, the illumination source 106 directs the illumination beam 108 to the sample along the illumination path 110. The illumination path 110 may include one or more beam conditioning elements 112 for modifying and / or adjusting the illumination beam 108. For example, the beam adjuster 112 may include, but is not limited to, a polarizer, a filter, a beam splitter, a diffuser, a homogenizer, an apodizer or a beam shaper. The illumination path 110 also includes one or more illumination path lenses 114 for controlling one or more characteristics of the illumination beam 108. For example, one or more illumination path lenses 114 may provide optical relays (eg, pupil relays, etc.). As another example, the one or more illumination path lenses 114 may modify the diameter of the illumination beam 108.

In another embodiment, the inspection system 100 includes a sample stage 116 for fixing and / or positioning the sample 102. Sample stage 116 is of any type known in the art for positioning sample 102, including, but not limited to, linear translation stages, rotational translation stages or translation stages with adjustable tips and / or tilts. May include stages.

In another embodiment, the inspection system 100 includes a detector 118 configured to capture the radiation emitted from the sample 102 via the collection path 120. For example, the detector 118 may receive an image of the sample 102 provided by an element in the collection path 120. As another example, the detector 118 may receive reflected, scattered (eg, through specular, diffuse reflection, etc.) or diffracted radiation from sample 102. As another example, the detector 118 may receive the radiation generated by the sample 102 (eg, the emission generated by absorption of the illumination beam 108, etc.). The collection path 120 may further include any number of optics for directing and / or modifying the illumination collected by the objective lens 104, which may include, but are not limited to, one or more collection path lenses 122. It may include one or more filters, one or more polarizers or one or more beam blocks.

The detector 118 may include any type of optical detector known in the art suitable for measuring the illumination received from the sample 102. For example, the detector 118 may include, but is not limited to, a CCD detector, a time delay integral (TDI) detector, a photomultiplier tube (PMT), an avalanche photodiode (APD), and the like. In another embodiment, the detector 118 may include a spectroscopic detector suitable for identifying the wavelength of radiation emitted from the sample 102.

In another embodiment, the inspection system 100 includes one or more visual field plane elements 124 arranged in the visual field plane. In this regard, the one or more field plane elements 124 selectively modify one or more properties of the radiation emitted from the sample based on the position from which the radiation from the sample is emitted. You may. For example, one or more field plane elements 124 may include a field diaphragm (eg, a diaphragm, etc.) to eliminate stray light and / or reduce the ghost image on the detector 118. In another embodiment, the collection path lens 122 may include a first collection path lens 122a for forming an intermediate image of the sample 102 in the field plane for placement of the field plane element 124.

In another embodiment, the inspection system 100 includes one or more pupillary elements 126 disposed within the pupillary. In this regard, the one or more pupillary elements 126 may selectively modify one or more properties of the radiation emitted from the sample based on the angle at which the radiation emitted from the sample 102 is emitted. For example, one or more pupillary elements 126 may include a phase plate to selectively modify the phase of the radiation based on the angle at which the radiation from the sample is emitted (eg, with respect to phase contrast imaging, etc.). As another example, the one or more pupillary elements 126 may include a transmission filter for selectively modifying the amplitude of radiation based on the angle at which radiation is emitted from the sample. In another embodiment, the collection path lens 122 may include a second collection path lens 122b for forming a relay pupil surface for the placement of the pupil surface element 126. In another embodiment, the collection path lens 122 may include a third collection path lens 122c (eg, a tube lens) for forming an image of the sample 102 on the detector 118.

In one embodiment, as shown in FIG. 1A, the inspection system 100 is oriented so that the objective lens 104 can simultaneously direct the illumination beam 108 toward the sample 102 and collect the radiation emitted from the sample 102. The beam splitter 128 may be included. In another embodiment, although not shown, the collection path 120 may include a separate element, for example, the illumination path 110 may use a first focusing element to focus the illumination beam 108 on the sample 102. The collection path 120 may collect radiation from sample 102 using a second focusing element. In this respect, the numerical apertures of the first focusing element and the second focusing element may be different. Further, as used herein, the inspection system 100 may facilitate multi-angle illumination of sample 102 and / or two or more illumination sources 106 (eg, coupled to one or more additional detectors). Attention is paid. At this point, the inspection system 100 may perform a plurality of measurements. In another embodiment, one or more optical components of the illumination path 110 and / or the collection path 120 are attached to a rotating arm (not shown) that pivots around the sample 102, resulting in a sample 102. The angle of incidence of the illumination beam 108 can be controlled by the position of the rotating arm.

In another embodiment, the inspection system 100 includes a controller 130. In another embodiment, the controller 130 includes one or more processors 132 configured to execute program instructions maintained within the memory medium 134. In this regard, one or more processors 132 of controller 130 may perform any of the various process steps described throughout this disclosure. In another embodiment, the controller 130 is communicably coupled to the detector 118. Therefore, the controller 130 may receive a collected signal from the detector 118 indicating the radiation emitted from the sample (eg, reflected radiation, scattered radiation, etc.). For example, one or more processors 132 of the controller 130 may detect and / or classify defects based on defect scattering characteristics based on the collected signal.

One or more processors 132 of the controller 130 may include any processing element known in the art. In this sense, one or more processors 132 may include any microprocessor type device configured to execute algorithms and / or instructions. In one embodiment, one or more processors 132 are configured to operate a desktop computer, a mainframe computer system, a workstation, an image computer, a parallel processor, or the inspection system 100 described throughout the disclosure. It can consist of any other computer system (eg, a network computer) that is configured to run the program. Further, it is recognized that the term "processor" can be broadly defined to include any device having one or more processing elements that execute program instructions from a non-temporary memory medium 134. Further, the steps described throughout this disclosure may be performed by a single controller 130 or by multiple controllers. Further, the controller 130 may include one or more controllers housed in one common housing or in multiple housings. Thus, any controller or combination of controllers can be individually implemented as a suitable module for incorporation into the inspection system 100. In addition, the controller 130 may analyze the data received from the detector 118 and feed the data to additional components within the inspection system 100 or outside the inspection system 100.

The memory medium 134 may include any storage medium known in the art suitable for storing program instructions that can be executed by one or more related processors 132. For example, the memory medium 134 may include a non-temporary memory medium. As another example, the memory medium 134 may include, but is not limited to, read-only memory, random access memory, magnetic or optical memory devices (eg, disks), magnetic tape, solid state drives, and the like. Further note that the memory medium 134 may be housed in one common controller housing with one or more processors 132. In one embodiment, the memory medium 134 may be located remotely to the physical location of one or more processors 132 and controller 130. For example, one or more processors 132 of the controller 130 may access remote memory (eg, a server) accessible through a network (eg, the Internet, an intranet, etc.). Therefore, the above description should not be construed as a limitation to the present invention, but merely as an example.

In the present specification, the optical properties of a material are _{defined by its complex refractive index n or complex relative permittivity ε = ε r} −iε _i = n ² , where ε _r and ε _i are the real and imaginary relative permittivity, respectively. Recognized as a department. FIG. 2 is a plot of complex relative permittivity 200 as a function of wavelengths of, but not limited to, semiconductor manufacturing, which may be related to defects, according to one or more embodiments of the present disclosure. .. As shown in FIG. 2, the dispersion curve representing the optical properties of the material as a function of wavelength is unique and can provide the basis for classifying the material composition of defects. However, classifying the material composition of defects based on the dispersion curve may be neither practical nor desirable in the manufacturing environment. For example, the sensitivity of the measurement can be limited by the spectral bandwidth available for small particles, as the scattered signal drops sharply (inversely proportional to the fourth power of the wavelength). As another example, variations in scatter ability as a function of wavelength can lead to further reduced sensitivity and / or throughput associated with longer measurement times.

Embodiments of the present disclosure cover, but are not limited to, simultaneous detection and classification of defects based on defect scattering properties such as scattering phase, scattering ability or defect absorption. Defect scattering properties provide a sensitive measure for the classification of defect material composition and can be measured using narrow band illumination sources (eg lasers) to efficiently utilize energy from the illumination source. In this regard, embodiments of the present disclosure can provide high sensitivity for both defect detection and classification.

であり、式中、αは粒子の半径であり、λは入射照明の（例えば、照明ビーム１０８等の）波長であり、εおよびε_ｍはそれぞれ欠陥および包囲媒体の比誘電率である。本明細書では、入射照明を散乱するサンプル上の異質粒子欠陥および構造的欠陥は両方とも、照明を散乱し得る小粒子として取り扱われ得る。 According to Rayleigh's model for elastic scattering by small particles (eg particles having a size much smaller than the wavelength of incident illumination), the scattering cross section is

In the equation, α is the radius of the particle, λ is the wavelength of the incident illumination (eg, illumination beam 108, etc.), and ε and ε _m are the relative permittivity of the defect and the surrounding medium, respectively. In the present specification, both foreign particle defects and structural defects on the sample that scatter the incident illumination can be treated as small particles that can scatter the illumination.

である。 The absorption cross section of such small particles

Is.

In addition, the phase of the scattered light associated with the small particles is

Equations (1) to (3) describe particle scattering and absorption in free space. For particles on the substrate (eg, in the context of wafer inspection), the scattering and absorption cross-sections are scaled by a factor (Q factor) that takes into account the coherent interaction of the reflection field from the substrate. However, the Q value is independent of the particle material properties and depends only on the substrate material properties. Therefore, the Q value has only a slight effect on the relative phase shift between particles of different materials and may be ignored when considering the relative scattering phase of foreign particle defects. The effect of the substrate on Rayleigh scattering is generally described in Germer, Applied Optics 36 (33), 8798, (1997), which is incorporated herein by reference in its entirety.

Scattering properties can be used to classify defect material compositions according to various scales and with a wide range of specificities. In one embodiment, defects can be classified based on the identification of one or more elements and / or compounds within the defect. For example, one or more elements and / or compounds within a defect can be identified based on measurements of any combination of scattering properties (eg, scattering phase, scattering ability, defect absorption, etc.). In another embodiment, defects can be classified based on material type, such as, but not limited to, metal, dielectric or organic materials. Defect classification by material type adequately determines further measures to be taken (eg, discarding the wafer, exposing the wafer to further cleaning steps based on the identification of the location of defects with different material types, material types, etc.). It may be enough for you.

In addition, samples in the manufacturing environment can be exposed to a limited number of known defect materials, which determines the number of scattering properties required to classify defects based on material composition or material type. Can be reduced. For example, measuring a single scattering property (eg, either the scattering phase or the ratio of scattering ability to defect absorption) may be sufficient to classify defects by a known subset of material or material type. In some cases.

FIGS. 3 and 4 and Table 1 provide representative data showing the classification of defects based on the scattering properties according to the inventive concept of the present disclosure. It should be noted that the data contained herein are provided for illustrative purposes only and should not be construed as limiting this disclosure in any way.

FIG. 3 is an absorption cross section plot 300 as a function of the scattering cross section of particles at a wavelength of 266 nm for different grain diameters based on the Rayleigh scattering model according to one or more embodiments of the present disclosure. In FIG. 3, different material types may be distinguished and classified based on absorption cross section and scattering cross section.

In one embodiment, defects are classified by material type based on absorption and scattering cross sections. For example, metals can have significantly stronger absorbency than dielectric metals, so that metals can be distinguished from dielectrics based on absorption and scattering cross sections. Further, as shown in FIG. 3, certain materials may have particularly large absorption sections that facilitate classification (eg silver (Ag), copper (Cu), gold (Au) or iron (Fe)). ..

In another embodiment, defects are classified by identifying defects within a group of materials that have similar absorption and / or scattering cross sections. For example, using the data in FIG. 3, the defects are the first group of materials, including silver (Ag), copper (Cu), gold (Au) or iron (Fe), and germanium (Ge), silicon (Si). Alternatively, it can be classified into a second group of materials containing tungsten (W) and a third group of materials containing silicon nitride (Si ₃ N ₄ ), silicon dioxide (SiO ₂ ) or water (H _{2 O).} Furthermore, it should be noted that the grouping of materials contained herein is provided for illustrative purposes only and should not be construed as limiting this disclosure. In a general sense, defects may be classified based on any number of groups of known materials.

In another embodiment, defects are classified by identifying the composition of at least one element and / or compound within the defect with high specificity based on absorption and / or scattering cross sections. The specificity at which defects can be classified may be related to the sensitivity and / or accuracy of the measurement of scattering properties and the differences in scattering properties with respect to known or predicted contaminants.

FIG. 4 is a plot of scattering phases 400 as a function of wavelengths of various materials, based on a Rayleigh scattering model, according to one or more embodiments of the present disclosure. According to FIG. 4, materials can be distinguished and classified based on the scattering phase measured with any number of suitable wavelengths of illumination. For example, the value of the scattering phase is zero in the case of a dielectric material having an actual refractive index (for example, SiO _{2 in FIG. 4).} Further, but not limited to, the value of the scattering phase of the additional material, such as metal, may vary such that the material composition of the defect can be determined by measuring the phase of the illumination scattered by the incident illumination. In one embodiment, defects can be classified based on measurements of scattering phase at a single wavelength. For example, the scattering phase can be measured at wavelengths where the scattering phase values of potential defects of interest can be distinguished. For example, silver (Ag), copper (Cu), gold (Au) and iron (Fe) present significantly higher scattering phase values at wavelengths of 266 nm than materials of additional interest, resulting in These materials can be easily detected and classified. In another case, the scattering phase values for many of the typical materials found in semiconductor processes can be easily distinguished at wavelengths of 193 nm.

Table 1 shows the relative permittivity, scattering cross section, absorption cross section and scattering phase for a 20 nm sphere of a typical material used in a semiconductor manufacturing process, based on a 266 nm illumination and Rayleigh scattering model according to one or more embodiments of the present disclosure. Includes a value. Defects may be classified based on any combination of scattering properties. For example, Table 1 further shows that dielectrics can induce a relatively low scattering phase shift in incident illumination, while metals can induce a significantly higher scattering phase, which is defect detection and It shows that it can be easily measured for classification purposes.

Any number of scattering properties may be measured at any number of wavelengths to provide the desired level of classification specificity. For example, the desired level of specificity can be achieved by measuring one or more scattering properties at a single wavelength. As another example, the desired level of specificity can be achieved by measuring a single scattering property at one or more wavelengths. Further, but not limited to, additional measurement techniques such as fluorescence imaging may be combined with the measurement of scattering properties to achieve the desired level of specificity.

As used herein, the description of scattering properties based on the Rayleigh scattering model provided in FIGS. 3 and 4 and Table 1 is provided for illustrative purposes only and should not be construed as limiting this disclosure. It is recognized that. Although the Rayleigh scattering model can provide physical insight into the scattering process, the scattering data produced by the Rayleigh scattering model can be limited. For example, a metal with a large negative value of _{real transmittance ε r and a small value of imaginary transmittance ε i} causes excitation of local surface plasmons that causes stronger scattering than predicted by the dipole-based Rayleigh scattering model alone. It is known to have a scattering resonance associated with. The surface plasmon resonance effect is described in general in Fan et al., Light: Science & Applications 3, e179 (2014), which is incorporated herein by reference in its entirety.

In a general sense, reference data related to classifying defects based on scattering properties may be obtained by any method known in the art. In another embodiment, the scattering properties may be modeled via computer simulation (eg, finite difference time domain (FDTD) simulation, etc.). In this regard, defects on the sample may be characterized based on a comparison of the measured scattering properties with the simulated scattering properties generated via computer simulation. In a further embodiment, the scattering properties of various defects of known size and composition may be measured to generate calibration reference data. Thereby, defects on the sample may be characterized based on the comparison of the measured scattering characteristics and the calibration data.

According to the inventive concept of the present disclosure, the scattering properties of defects are limited, but by a plurality of measurement techniques such as interferometry techniques, sample imaging, or point-by-point scanning imaging techniques. May be measured.

In one embodiment, the defect illuminates the sample with an illumination beam and uses multiple detection modes to detect radiation emitted from the sample (eg, scattered and / or reflected radiation) and is based on multiple detection modes. It is detected and classified based on determining the scattering characteristics and classifying the defects based on the scattering characteristics. The detection mode may include, but is not limited to, a particular configuration of the phase plate in interferometric measurements, generation of a brightfield image, generation of a darkfield image, or measurement of a sample in a controlled immersion medium. In this regard, detecting the radiation emitted by the sample in multiple detection modes can facilitate the measurement of one or more scattering properties of defects on the sample.

With general reference to FIGS. 1A-1F, the inspection system 100 may include a detection mode device 136 for modifying the detection mode of the inspection system 100.

In one embodiment, defects are detected and classified using phase contrast imaging. Phase contrast imaging can provide a stable common path interferometer comparable to image-based optical inspection tools. Thereby, phase contrast imaging can be very suitable for the manufacturing environment. Phase-shifted phase-contrast imaging is generally described in US Pat. No. 7,295,303, granted November 13, 2007, which is incorporated herein by reference in its entirety.

式中、Ｐ_ｒｅｆは反射光に関連する信号であって、干渉計の基準アームとして考慮されてよく、Ｐ_ｓは散乱光の強度であり、φ_ｒｅｆは全粒子に共通の反射光の位相であり、φ_ｓは散乱光の位相であり、φ_０は反射光と散乱光の間の調整可能な位相シフトである。 In phase contrast imaging, the peak signal of particle scattering is given by the interference between specular and scattered light.

In the equation, _Pre is a signal related to reflected light and may be considered as a reference arm of an interferometer, P _s is the intensity of scattered light, and φ _ref is the phase of reflected light common to all particles. Yes, φ _s is the phase of the scattered light, and φ ₀ is the adjustable phase shift between the reflected and scattered light.

In addition, the scattering properties associated with defects on the sample can be measured via phase shift phase contrast imaging. In this regard, multiple collection signals are obtained for a series of measurements (eg, in connection with multiple detection modes), where φ ₀ differs by a known amount for each measurement.

式中、δφ_ｓ＝φ_ｒｅｆ−φ_ｓは、散乱光と反射光の間の位相差である。散乱位相は、Ｎ個の収集信号から、以下に従って抽出され得る。

式中、

および、

である。 N measurements (eg, N detection modes) may yield N, but not required, collection signals, in which case φ ₀ is N equal phase steps in one 2π phase cycle. fluctuate. In this case, the particle collection signal at each phase step can be described as:

In the equation, δφ _s = φ _ref −φ _s is the phase difference between the scattered light and the reflected light. The scattering phase can be extracted from the N collected signals according to the following.

During the ceremony

and,

Is.

When N = 4, equations (6)-(8) are divided into the following.

および

In addition to the scattering phase, scattering ability and absorption can be extracted from the N-collected signal as follows.

and

In addition, defect absorption is provided by:

および

式中、Ｉ_０は、サンプル１０２に入射する照明ビーム１０８の強度である。

および

In addition, scattering ability and defect absorption can be described as:

and

In the equation, I ₀ is the intensity of the illumination beam 108 incident on the sample 102.

and

Therefore, the scattering phase can also be obtained by:

_{The relative phase shift φ 0} between the radiation specularly reflected by the sample and the radiation scattered by the sample is adjusted by any technique known in the art and is associated with N known values of _{phase offset φ 0.} N collection signals may be provided.

In one embodiment, the detection mode device 136 of the inspection system 100, with respect to the generation of the N acquisition signal on the detector 118 associated with N different values phi ₀ of the phase offset, N a pupil plane of the inspection system 100 It is configured to sequentially provide a number of different phase plates. In this respect, N different phase plates may correspond to the pupil surface element 126 of the inspection system 100.

The N different phase plates may be physically arranged on different substrates or may be physically arranged on a common substrate. Further, the detection mode device 136 may provide N different phase plates to the pupil surface by any method known in the art. In one embodiment (not shown), the detection mode device 136 includes a translation stage (eg, a linear translation stage, a rotational translation stage, etc.) for translating the N phase plates to the pupil plane. In another embodiment (not shown), the detection mode device 136 may include a variable phase plate that can provide an adjustable phase shift as a function of position on the variable phase plate. In one example, the variable phase plate may include a liquid crystal element. In another case, the variable phase plate may include an electro-optical crystal capable of introducing a voltage-controllable adjustable phase shift.

In another embodiment, the detection mode device 136 may include a series of beam splitters that split the radiation emitted from the sample 102 into N different beam paths. In this regard, the detection mode device 136 is a pupil plane of the N different beam paths may provide different stationary phase plate having a different phase offset phi _0. Furthermore, detector 118 can include a detector assembly positioned on each N different beam paths to provide N acquisition signals associated with N different phase offset phi _0. FIG. 1B is a conceptual diagram of an inspection system 100 including four stationary phase plates according to one or more embodiments of the present disclosure. As shown in FIG. 1B, the detection mode device 136 may include a beam splitter that splits the radiation emitted from the sample into four beam paths, including four phase plates on the pupil plane of the four beam paths. In this regard, the phase plate may be the pupillary element 126 of the system. Furthermore, the 4 phase plates four different known phase offset phi ₀ (e.g. 0 °, 90 °, 180 ° and 270 °) may provide. In another embodiment, the detector 118, the N for defect detection and classification phase offset phi ₀ and associated N-collection signal four arranged in four beam paths to produce a The detector assembly 118a-118d may be included.

FIG. 1C is a conceptual diagram of the phase shift phase contrast imaging inspection system 100 according to one or more embodiments of the present disclosure, in which the relative phases of the specularly reflected radiation 138 and the scattered radiation 140 by the sample are controlled by the phase plate. ..

_{In a general sense, the phase plate in the pupil plane has a relative phase φ 0} between the specular reflection line and the scattered radiation when the specular reflection line and the scattered radiation are at least partially distinguishable in the pupil plane. It may be modified selectively. For example, the inspection system 100 has a limited angular range by limiting the distribution of the illumination beam 108 in order to select the position of the objective lens 104 in the pupil plane (eg, the posterior focal plane of the objective lens 104). It may be configured to illuminate sample 102. The specular radiation is then limited to a complementary range of positions within the pupil plane, while the scattered radiation may be present at any angle within the pupil plane. At this point, the phase plate in the pupil plane selectively corrects the relative phase between the specular reflection line and the scattered radiation based on the position of the specular reflection line and the scattered radiation in the pupil plane. Note that some scattered radiation is affected by the phase plate, but the effect on the measurement is insignificant.

The inspection system 100 may provide any distribution of the illumination beam 108 suitable for illuminating the sample 102 in a limited angular range. For example, the inspection system 100 may provide the illumination beam in an annular profile with one or more lobes and the like. FIG. 1D is a conceptual diagram of an illumination beam with an annular profile for phase-shifted phase contrast imaging according to one or more embodiments of the present disclosure. The annular profile may provide uniform radial illumination of the sample to avoid shadowing artifacts. In addition, the annular profile near the numerical aperture (NA) edge of the objective lens 104 provides the highest angle of incidence achievable by the objective lens 104, which promotes the strongest scattering from defects and is small. It can be particularly advantageous for particle detection and classification.

The desired distribution of the illumination beam 108 may be generated by any method known in the art. For example, the annular distribution shown in FIG. 1C is not essential, but a diffractive optic to reshape the illumination from the illumination source 106 with an annular diaphragm to block unwanted light directly by the illumination source 106. (DOE) may be produced by a holographic diffuser to reshape the illumination from the illumination source 106, or by a bundle of fibers arranged in an annular profile.

In another embodiment, the one or more illumination path lenses 114 relay the distribution of the desired illumination beam 108 to the posterior focal plane of the objective lens 104 to provide a desired range of illumination angles for the sample 102. good. Similarly, one or more collection path lenses 122 (eg 122b and / or 122a) relay the posterior focal plane of the objective lens 104 and by means of a phase plate normal reflected radiation (eg, forward reflected radiation 138 in FIG. 1C). ) And the scattered radiation (eg, the scattered radiation 140 in FIG. 1C) may provide a relay pupil surface suitable for correction of the relative phase.

Equation (4) and (5) contrast of interferometry signals provided by the phase contrast imaging as described, the relative strength of the positive reflected radiation at the detector 118 (e.g., P _ref) and scattered radiation (e.g. P _s) May be proportional to. The intensity of scattered radiation can be significantly lower than the intensity of specular radiation, especially for small particles. In another embodiment, the pupillary element 126 of the inspection system 100 reduces the intensity of specular radiation against scattered radiation to facilitate high contrast interferometry signals for sensitive particle detection and classification. , Includes a transmission filter. For example, the transmission filter may be placed in close proximity to any of the N phase plates provided by the detection mode device 136. As another example, a set of N transmission filters may be integrated into N phase plates.

Still referring to FIG. 1C, in another embodiment, the inspection system 100 samples 102 with an incoherent illumination beam 108 to avoid artifacts associated with imaging with a coherent beam (eg, speckle artifacts, etc.). Illuminate. In one example, the illumination source 106 may directly provide the incoherent illumination beam 108. For example, the illumination source 106 may include an incoherent lamp illumination source. In addition, the incoherent illumination source 106 may include a filter for controlling the output spectrum of the illumination beam 108. In another example, the illumination source 106 may provide a coherent illumination beam 108 (eg, a laser) and the inspection system 100 may include one or more elements for removing coherence. For example, one or more beam adjusting elements 112 may include a dynamic diffuser (eg, a speckle buster).

In another embodiment, the beam adjusting element 112 of the inspection system 100 includes a polarizer for controlling the polarization of incident illumination to the inspection system 100. For example, the beam conditioning element 112 may include a radial polarizer to provide consistent p-polarized light for all azimuth angles of illumination incident on sample 102. It is recognized herein that the polarization state can be adjusted based on the expected type of defect that is to be detected and classified by the inspection system 100. Therefore, the beam adjusting element 112 may include any type of polarizer.

Figure 5 is a plot 500 of FDTD simulation of various phase shifting the phase contrast signal of 20nm particles of common foreign matter at a wavelength of 266nm as a function of one or more embodiments of the phase offset of the present disclosure (e.g., phi ₀₎ including. In particular, plot 500 shows iron (Fe), silicon dioxide (SiO ₂ ), copper (Cu), silicon nitride (Si ₃ N ₄ ) and aluminum (Al) with _{respect to 15 phase offsets φ 0 (eg N = 15).} Includes FDTD simulation of the phase shift phase contrast signal of. In addition, Plot 500 was simulated with an annular illumination beam with a central NA of 0.85, with 10% attenuation of specular radiation relative to scattered radiation using a 0.9NA objective. Plots 502-508 include images of particles on the sample simulated with phase offsets of 0, 90, 180 and 270 degrees, respectively. As shown in plot 500, a series of phase shift phase contrast signals generated with a series of known phase offsets between specular and scattered radiation provides a vibration signal for each material from which the scattered phase can be extracted. In particular, compared to dielectric silicon dioxide and silicon nitride, the relative phase shift between metallic copper and iron fits well with the calculations generated using the Rayleigh scattering model in Table 1. In addition, the aluminum particles have a larger phase shift than that predicted by the Rayleigh scattering model due to the excitation of localized surface plasmons predicted by the FDTD simulation.

式中、ｚは焦点ずれ（例えば、公称焦点位置からのサンプルの位置の変動）であり、ｓｉｎθは、正規化された瞳半径である。散乱光の位相オフセットはさらに、以下として概算され得る。

式中、θ_ｒは正反射放射線の極角であり、θ_ｓは対物レンズ１０４によって収集された散乱放射線の極角の加重平均を表す。 Referring again to FIG. 1A, in one embodiment, the phase offset phi ₀ between scattered radiation and specular reflection line additionally, the focal position of the sample stage 116, be varied along the optical axis of the objective lens 104 Can be controlled by. In this regard, the detection mode device 136 may include a sample stage 116 so that the detection mode device 136 can control the focal position of the sample 102. The phase offset due to defocus can be described as a function of the imaging pupil position.

In the equation, z is the defocus (eg, the variation of the sample position from the nominal focal position) and sinθ is the normalized pupil radius. The phase offset of the scattered light can be further estimated as:

In the equation, θ _r is the polar angle of specularly reflected radiation, and θ _s is the weighted average of the polar angles of the scattered radiation collected by the objective lens 104.

FIG. 6 is a plot 600 of a measured phase shift phase contrast signal of 100 nm particles of various common foreign bodies as a function of sample focal position according to one or more embodiments of the present disclosure. In particular, plot 600 relates to two 100 nm gold (Au) spheres and two 100 nm silicon dioxide (SiO ₂ ) spheres for a 13-value sample position (eg N = 13) using laser illumination at a wavelength of 266 nm. The measured phase shift phase contrast signal is included. In addition, plot 600 was generated with an annular illumination beam in the NA range of 0.75 to 0.85 using a 0.85 NA objective. Plots 602-610 include phase shift phase contrast images of the measuring spheres on the sample at defocus values of −0.4 μm, −0.2 μm, 0 μm, 0.2 μm and 0.4 μm, respectively. As shown in plot 600, a series of phase shift phase contrast signals generated with a series of known phase offsets between the positive reflection line and the scattered radiation (eg, generated by adjusting the focal position of the sample) , Provides vibration signals for each material from which the scattering phase can be extracted. FIG. 6 clearly shows the significant difference in scattering phase between gold particles and silicon dioxide spheres so that phase-shifted phase contrast imaging can detect and classify defects.

FIG. 7 is a plot 700 containing FDTD simulations of 100 nm particles of gold, silicon dioxide and copper under the same conditions as the data shown in FIG. 6 according to one or more embodiments of the present disclosure. Comparison of plots 600 and 700 reveals a good correlation between measurements and simulation data. In this respect, phase shift phase contrast imaging can detect and distinguish defects formed from different materials. Therefore, phase shift phase contrast imaging signals can be used to classify defects according to material type or material composition.

With reference to FIGS. 1E and 1F, phase shift phase contrast imaging may be used in a coherent imaging system. FIG. 1E is a conceptual diagram of an inspection system 100 for phase shift phase contrast imaging using coherent illumination according to one or more embodiments of the present disclosure. In one embodiment, the inspection system 100 provides at least one collimated illumination beam 108 at an off-axis position on the posterior focal plane of the objective lens 104 such that the illumination beam 108 is incident on the sample 102 at high NA. Thus, the pupil plane of the collection path 120 will include at least one collimated beam associated with specular radiation at a limited location in the pupil plane and scattered radiation at any other location within the pupil plane. .. Therefore, the detection mode device 136 may provide a set of N phase mask leading to the N known value of phase offset phi ₀ between scattered radiation and specular reflection lines. For example, as described above, the detection mode device 136 may sequentially translate N phase masks to the pupil surface. As another example, as described above, the detection mode device 136 emits N beams of radiation emitted from sample 102 for parallel detection of N collection signals associated with N values of _{φ 0.} It may include a series of beam splitters that split into paths. It is noted herein that the simultaneous measurement of multiple phase-shifted phase contrast signals of this type can provide highly efficient throughput for defect detection and classification.

In another embodiment, one or more TDI imaging sensors are used to detect one or more phase shift phase contrast signals to provide a line scan image of the sample and associated defects. Since coherent imaging artifacts (eg, speckle artifacts) can be negligible in point-by-point imaging configurations, the illumination source 106 in FIG. 1E may further generate an incoherent illumination beam 108.

In another embodiment, the pupillary element 126 of the inspection system 100 may include a polarizer mask to suppress scattering from the surface of the sample. In this respect, the polarizer mask can increase the detection sensitivity of phase shift phase contrast imaging on small particles. In the present specification, the polarizations of various components of the radiation emitted from the sample (eg, specular radiation, radiation scattered by defects, radiation scattered by the sample, etc.) are different from each other and vary over the NA of the objective lens 104. It is recognized that it can be done. Therefore, the collection path 120 is derived from a polarizer (for example, a linear polarizer having a constant polarization direction over NA, a mirror-symmetrical polarizer having two different polarization directions symmetrically dispersed over NA, etc.) and a sample. It may include a polarizer mask configured to selectively transmit one or more desired components of emitted radiation. The use of a polarizer mask to suppress surface scattering is described in US Pat. No. 8,891,079 granted on November 18, 2014 and US Patent Application Publication No. 2016 published on April 7, 2016. It is described in general at / 0907727, both of which are incorporated herein by reference in their entirety.

FIG. 1F is a simplified schematic diagram of a polarizer mask 142 according to one or more embodiments of the present disclosure. In one embodiment, the polarizer mask 142 includes a transmission region 144 and a blocking region 146. Further, the blocking region 146 may include one or more attenuated transmission regions through which a portion of specular radiation 138 can pass. Thus, specular radiation 138 and scattered radiation 140 associated with defect scattering (not shown) can be transmitted, whereas radiation scattered by the surface of the sample (eg, which constitutes noise in phase shift phase contrast measurements). Can be blocked.

With reference to FIG. 1A in general again, the inspection system 100 may measure scattering properties, including scattering ability and defect absorption, without measuring the scattering phase. Such measurements may be used alone for defect detection and classification, or may be used in combination with the scattering phase measurements described above herein.

In one embodiment, defects are detected and classified based on measurements of scatter potential and defect absorption associated with the bright and dark field images of the sample. For example, the inspection system 100 may provide a brightfield image with any distribution of the illumination beam 108 and an open (eg, unobstructed or minimally obstructed) pupil surface. The signal intensity thus associated with each point of the brightfield image corresponds to the reflectance of the corresponding portion of the sample, and the signal intensity associated with the defect may be associated with the light loss due to this absorption. In this regard, a brightfield image (or vice versa) may provide a measurement of the absorption cross section of a defect on the sample.

In contrast, a darkfield image can be obtained using the complementary distribution of the illumination beam 108 and the mask on the pupil surface. At this point, specular radiation from the sample is blocked in the pupil and scattered radiation is transmitted in the pupil. Therefore, the signal intensity associated with the defect can correspond to the scattering power of the defect.

In another embodiment, the detection mode device 136 of the inspection system 100 sequentially modifies the transmittance of the pupil surface to obtain a brightfield image as a brightfield collection signal and a darkfield collection signal for defect detection and classification. Provides a darkfield image as. For example, the inspection system 100 may provide a fixed illumination beam 108 suitable for both brightfield and darkfield detection modes (eg, annular distribution, single or multilobe distribution, etc.). In addition, the detection mode device 136 sequentially provides an open aperture and a cutoff aperture so that the detector 118 can provide brightfield and darkfield acquisition signals for defect detection and classification based on scatter ability and defect absorption. The distribution of the illumination beam 108 may be complemented.

The brightfield and darkfield diaphragms may be physically located on different or common substrates. Further, the detection mode device 136 may provide a brightfield diaphragm and a darkfield diaphragm on the pupil surface by any method known in the art. In one embodiment (not shown), the detection mode device 136 includes a translational stage (eg, a linear translational stage, a rotational translational stage, etc.) that translates the diaphragm into the pupil plane. In another embodiment (not shown), the detection mode device 136 may include a variable aperture that may provide adjustable transmission as a function of the position of the variable aperture. In one example, the variable phase plate may include a liquid crystal device.

In another embodiment, the detection mode device 136 may modify both the transmittance of the pupil surface and the distribution of the illumination beam 108 to provide a brightfield detection mode and a darkfield detection mode. For example, the detection mode device 136 may have an aperture of the illumination path 110 to the pupil surface for correction of the distribution of the illumination beam 108 and a collection path 120 to correct the transmission of radiation emitted from the sample to the detector 118. A diaphragm on the pupil surface may be provided.

In one embodiment, defects are detected and classified based on a comparison of multiple images of the sample, in which the index of refraction of the immersion medium surrounding the sample is corrected. The scattering cross section of a defect and therefore the intensity of the scattered signal can vary based on the index of refraction of the immersion medium and, in particular, the difference between the index of refraction of the defect and the immersion medium. Table 2 shows the ratio of Rayleigh scattered cross sections of common defective materials in the water immersion imaging mode and the dry imaging mode at 193 nm and 266 nm according to one or more embodiments of the present disclosure.

As shown in Table 2, defects are classified based on the ratio of scattering power measured in water and dry immersion. In particular, metal particles can be distinguished from dielectrics or weakly absorbent materials. For example, the actual index of refraction of many dielectrics (eg, SiO ₂ ) is significantly closer to water than many metals (eg, Al, Au, etc.), resulting in the ratio of scattered cross sections in water immersion and dry imaging. Can be significantly lower for dielectrics than for metals.

In another embodiment, the detection mode device 136 of the inspection system 100 sequentially modifies the immersion medium surrounding the sample to include two or more immersion media with a known index of refraction. In this regard, the detector 118 may generate two or more collection signals associated with imaging the sample in two or more immersion media. The immersion medium may be a liquid (eg, water, immersion oil, etc.) or a gas (open air, nitrogen, argon, etc.). For example, the detection mode device 136 may include a chamber containing a sample and an immersion medium. Further, the detection mode device 136 may include, but is not limited to, an immersion medium transfer device such as a container, tube, pump, valve or pressure regulator.

Tables 3 and 4 show experimental measurements of the scattering power of 100 nm spheres of gold and silicon dioxide in darkfield water immersion in annular illumination at a wavelength of 266 nm and in dry imaging mode according to one or more embodiments of the present disclosure. I will provide a.

Comparing the experimental data in Tables 3 and 4 with the simulation data in Table 2, it becomes clear that the measured data are in good agreement with the simulation. Therefore, defects can be easily classified based on a comparison of scattering powers measured in multiple imaging modes, with each imaging mode corresponding to an image in a different immersion medium.

FIG. 8 is a flow chart illustrating steps performed by Method 800 for detecting and classifying defects based on defect scattering properties according to one or more embodiments of the present disclosure. Applicants note that embodiments and enablement techniques previously described herein in the context of System 100 should be construed as extending Method 800. However, it is also noted that the method 800 is not limited to the structure of the inspection system 100.

In one embodiment, method 800 includes step 802 of illuminating the sample with an illumination beam. The illumination beam may include illumination of any wavelength, including but not limited to VUV, DUV, UV, visible or IR wavelengths. Further, the illumination beam may be spatially coherent or spatially incoherent. For example, a spatially coherent beam (eg, a laser source, etc.) can provide a highly efficient use of spectral power in point-by-point imaging. As another example, a spatially coherent beam (eg, a lamp source, a speckle-busted laser source, etc.) may illuminate the extended portion of the sample for extended imaging.

Illumination of the sample induces the sample to radiate radiation. For example, when illuminated by an illumination beam, the sample may reflect radiation (eg specular), scatter radiation (eg by one or more defects) and / or diffract radiation. As used herein, diffracted radiation from a sample can indicate the frequency of a feature on the sample, as small features can produce higher diffraction orders than relatively large features within a given solid angle. Is recognized.

In one embodiment, step 802 comprises illuminating the sample at an angle (eg, high NA, etc.) such that one or more non-zero diffraction orders are emitted from the sample.

In another embodiment, Method 800 includes step 804 to collect illumination from a sample using two or more detection modes to generate two or more detection signals. In another embodiment, Method 800 includes step 806 to determine one or more defect scattering properties associated with radiation emitted from a sample based on two or more collected signals. In another embodiment, Method 800 includes step 808 to classify one or more defects based on one or more scattering properties associated with the defects on the sample.

Defect scattering properties can include, but are not limited to, scattering phase, scattering ability and defect absorption. In a general sense, scattering properties vary based on the composition of the defect. Therefore, the composition of defects can be determined by measuring the defect scattering properties. In addition, defects can be classified based on the measured defect scattering properties. For example, defects can be categorized by common material types (eg, metals, dielectrics, organics, etc.) based on the identification of one or more elements and / or compounds within the defect or based on the sensitivity of measurement. A known set of materials may be known or generally expected to be present as a defect. In such cases, a limited number of materials may reduce the measurement sensitivity required to classify defects according to the desired particle size.

In one embodiment, defect scattering properties associated with defects on one or more samples are determined based on measurements with a narrowband illumination source. In another embodiment, short wavelength illumination (eg, VUV wavelength, DUV wavelength, UV wavelength, etc.) is highly scatterable and efficient in the spectral power of the illumination source based on ^{the λ-4 dependence of the scatterability on the wavelength.} Can be utilized by method 800 to provide effective use.

For example, step 804 may include collecting radiation emitted from the sample using multiple detection modes to provide at least the scattering phase associated with defects on the sample.

In one embodiment, step 804 comprises measuring multiple phase contrast images of a sample based on the interference between specular and scattered radiation from the sample to provide phase shift phase contrast imaging. In that case, step 804 may include deliberately introducing a series of known phase offsets between specular and scattered illuminations to generate a phase contrast interference image for each known phase offset. Step 806 may then include determining any of the scatter phase, scatter potential and / or defect absorption associated with the defect on the sample based on a series of phase contrast images. In addition, step 808 may include classifying defects on the sample based on scattering phase, scattering ability and / or defect absorption. In addition, detection of multiple acquired signals related to known phase offsets introduced into phase shift phase contrast imaging can be performed sequentially or simultaneously.

In another embodiment, step 804 includes measuring at least a brightfield image and a darkfield image of the sample. Step 806 may include at least brightfield and darkfield image-based determination of scatter potential and / or defect absorption associated with defects on the sample. For example, a brightfield image can provide absorption of defects on a sample (eg, an absorption cross section), whereas a darkfield image can provide the scattering power of a sample (eg, a scattering cross section). Step 808 may then include classifying defects based on scatter ability and / or defect absorption.

In another embodiment, step 804 comprises measuring a sample surrounded by at least two different immersion media (eg, ambient air, water, immersion oil, etc.). The scatter ability of defects can be a function of the difference in refractive index of the immersion medium. In step 806, the scattering cross section (based on scattering ability) can be measured for each medium. Accordingly, the ratio of the measured scattering cross sections of the defects measured in the two different immersion media is calculated in step 808 to classify the defects.

The subject matter described herein refers to different components that are sometimes contained within, or that are connected to other components. It should be understood that such depicted structures are merely representative and, in fact, many other structures that achieve the same functionality can be implemented. In a conceptual sense, any arrangement of components that achieve the same functionality is effectively "coordinated" to achieve the desired functionality. Thus, any two components combined herein to achieve a particular functionality, whether structural or intermediate, are "coordinated" with each other to achieve the desired functionality. Can be considered. Similarly, any two components so linked are also seen to be "connected" or "joined" to each other to achieve the desired functionality and can be so linked. Any two components appear to be "combinable" with each other to achieve the desired functionality. Specific examples of combinable examples include, but are not limited to, physically interactable and / or physically interacting components and / or radio-interactable and / or radio-interacting components and / or. Includes logically interactable and / or logically interacting components.

Much of this disclosure and its associated benefits will be understood from the above description and the components of the disclosure without deviating from the subject of the disclosure or at the expense of all of its material interests. It will be clear that it can be done in the form, structure and arrangement of. The forms described are merely explanations, and the claims below are intended to include such changes. Furthermore, it should be understood that the present invention is defined by the appended claims.

Claims (51)

It ’s a system,
With an illumination source configured to generate an illumination beam,
With one or more focusing lenses configured to direct the illumination beam to the sample,
With the detector
One or more collection lenses configured to direct the radiation emitted from the sample towards the detector, the radiation emitted from the sample being scattered by the sample and the radiation specularly reflected by the sample. With one or more collection lenses containing the radiation
The detector is configured to generate two or more collected signals by introducing two or more different selected phase offsets between the radiation specularly reflected by the sample and the radiation scattered by the sample. With one or more phase plates,
A controller that is communicably coupled to the detector and includes one or more processors.
The one or more processors
Determining one or more scattering phase values introduced into an illumination beam scattered by one or more defects on the sample based on the two or more collected signals, and determining the one or more defects. Classification based on one or more of the scattering phase values according to a set of predetermined defect classifications.
A system configured to execute a program instruction configured to instruct the one or more processors. The one or more phase plates
The translation stage comprises two or more phase plates attached to a translational stage communicatively coupled to the controller, wherein the translational stage sequentially inserts the two or more phase plates into radiation emitted from the sample. Configured to introduce two or more selected phase offsets, the two or more collected signals respond in response to the radiation emitted by the sample being modified by the two or more phase plates. The system according to claim 1, which corresponds to two or more signals sequentially generated by the detector. Further including one or more beam splitters that split the radiation emitted from the sample into two or more sample beams.
The one or more phase plates include two or more phase plates.
The two or more sample beams are directed at the two or more phase plates to introduce two or more selected phase offsets, and the two or more collected signals are sampled by the two or more phase plates. The system of claim 1, wherein the radiation emitted from the detector corresponds to two or more signals generated by the two or more detector assemblies of the detector in response to being modified. The translation stage comprises a translation stage for fixing the sample, the translation stage is communicatively coupled to the controller, and the translation stage has two or more focal positions of the sample along the optical axis of the one or more focusing lenses. The two or more collected signals are two or more generated by the detector at the two or more focal positions, configured to translate into and introduce the two or more different selected phase offsets. The system according to claim 1, which corresponds to the above signals. The detection mode controller
A brightfield image on the detector as a first collection signal of the two or more collection signals based on radiation emitted from the sample and the said as a second collection signal of the two or more collection signals. The system of claim 1, further comprising one or more diaphragms configured to sequentially create a darkfield image on the detector. The system of claim 1, wherein at least the first signal of the two or more collection signals comprises a dry image and at least one of the two or more collection signals comprises a water immersion image. The system of claim 1, further comprising an attenuating plate configured to reduce the intensity of the illumination specularly reflected by the sample relative to the illumination scattered by the sample. The set of predetermined defect classifications
The system of claim 1, comprising at least one of a metal, dielectric or organic material. The set of predetermined defect classifications
The system according to claim 1, wherein the system comprises at least one of silver, aluminum, gold, copper, iron, molybdenum, tungsten, germanium, silicon, silicon nitride and silicon dioxide. The radiation emitted from the sample further comprises fluorescent radiation, and the one or more processors further include.
One or more fluorescence intensity values associated with illumination generated by one or more defects on the sample are determined based on the two or more collected signals.
The system of claim 1, wherein the one or more defects are classified according to a set of predetermined defect classifications based on the one or more fluorescence intensity values. The system according to claim 1, wherein the illumination beam includes an annular illumination beam. 11. The system of claim 11, wherein the illumination beam comprises a spatially coherent illumination beam. 11. The system of claim 11, wherein the illumination source comprises a narrowband illumination source. 13. The system of claim 13, wherein the illumination source comprises a speckle-removing laser source. 11. The system of claim 11, wherein the illumination source comprises a broadband illumination source. 15. The system of claim 15, wherein the broadband illumination source comprises an incoherent lamp source. 15. The system of claim 15, wherein the broadband illumination source comprises an adjustable broadband illumination source. 11. The system of claim 11, wherein the illumination beam comprises a spatially coherent illumination beam. 18. The system of claim 18, wherein the illumination beam comprises a laser source. 19. The system of claim 19, wherein the laser source comprises an adjustable laser source. In the pupil surface of the one or more collecting lenses, the system is further configured to suppress the illumination scattered by the surface of the sample with respect to the illumination scattered by the one or more defects on the sample. The system of claim 1, further comprising a polarizer mask. 21. The system of claim 21, wherein the illumination beam comprises a single collimated illumination beam. 21. The system of claim 21, wherein the detector comprises a time delay integral (TDI) detector. The system according to claim 1, wherein the one or more focusing lenses and the one or more collecting lenses share at least one common lens. The one or more phase plates include a variable phase plate attached to a translational stage communicably coupled to the controller, the translational stage positions the variable phase plate with respect to the radiation emitted from the sample. It is configured to sequentially modify to introduce the two or more selected phase offsets, and the two or more collected signals react to the radiation emitted from the sample being modified by the variable phase plate. The system according to claim 1, wherein the two or more signals are sequentially generated. It ’s a system,
With an illumination source configured to generate an illumination beam,
With one or more focusing lenses configured to direct the illumination beam to the sample,
With the detector
One or more collection lenses configured to direct the radiation emitted from the sample towards the detector, the radiation emitted from the sample being specularly reflected by the sample and scattered by the sample. With one or more collection lenses, including
A translational stage that fixes the sample, wherein the translational stage translates the sample to two or more focal positions along the optical axis of the one or more focusing lenses and the radiation that is positively reflected by the sample. Introducing two or more different selected phase offsets with the radiation scattered by the sample, the detector is configured to generate two or more acquired signals at the two or more focal positions. Translated stage and
A controller that is communicably coupled to the detector and the translational stage and includes one or more processors, the one or more processors.
One or more scattering phase values introduced into the illumination beam scattered by one or more defects on the sample are determined based on the two or more collected signals.
The one or more defects are classified based on the one or more scattering phase values according to a set of predetermined defect classifications.
A system configured to execute a program instruction configured to instruct the one or more processors. It ’s a system,
With an illumination source configured to generate an illumination beam,
With one or more focusing lenses configured to direct the illumination beam to the sample,
With the detector
One or more collection lenses configured to direct the radiation emitted from the sample towards the detector, the radiation emitted from the sample being specularly reflected by the sample and scattered by the sample. With one or more collection lenses, including
A brightfield image is generated as a brightfield acquisition signal on the detector based on the radiation emitted from the sample, and a darkfield image is generated on the detector based on the radiation emitted from the sample. A detection mode controller configured to sequentially generate
A controller that is communicably coupled to the detector and includes one or more processors.
The one or more processors
To detect one or more defects on a sample by comparing the brightfield acquisition signal with the darkfield acquisition signal.
Determining the defect absorption value for the one or more defects based on the signal strength of the one or more defects in the brightfield acquisition signal.
The scattering intensity value for the one or more defects is determined based on the signal intensity of the one or more defects in the darkfield acquisition signal, and the one or more defects are classified into a set of predetermined defect classifications. According to, classification based on the defect absorption value and the scattering intensity value,
A system configured to execute a program instruction configured to instruct the one or more processors. It ’s a system,
With an illumination source configured to generate an illumination beam,
With one or more focusing lenses configured to direct the illumination beam to the sample,
With the detector
One or more collection lenses configured to direct the radiation emitted from the sample towards the detector, the radiation emitted from the sample being scattered by the sample and the radiation specularly reflected by the sample. With one or more collection lenses containing the radiation
A chamber configured to house the sample and the immersion medium,
A controller that is communicably coupled to the detector and includes one or more processors.
The one or more processors
Receiving a dry collection signal from the detector generated by the immersion medium containing a gas,
Receiving the immersion collection signal from the detector generated by the immersion medium containing the liquid,
The dry collection signal is compared to the immersion collection signal to detect one or more defects on the sample, and the one or more defects are detected in the dry collection signal according to a set of predetermined defect classifications. And classification based on the comparison of the immersion collection signals,
A system configured to execute a program instruction configured to instruct the one or more processors. Defect classification method
Illuminating the sample with an illumination beam and
By collecting the illumination emitted from the sample using two or more detection modes, the radiation emitted from the sample is specularly reflected from the sample and the radiation scattered from the sample. To include,
Introducing two or more different selected phase offsets between the radiation specularly reflected from the sample and the radiation scattered from the sample to generate two or more captured signals.
Determining one or more defect scattering phase values introduced into the illumination beam scattered by one or more defects on the sample based on the two or more collected signals.
Including classifying the one or more defects based on the one or more defect scattering phase values according to a selected set of predetermined defect classifications.
Defect classification method. It ’s a system,
With an illumination source configured to generate an illumination beam,
With one or more focusing lenses configured to direct the illumination beam to the sample,
With the detector
One or more collection lenses configured to direct the radiation emitted from the sample towards the detector, the radiation emitted from the sample being scattered by the sample and the radiation specularly reflected by the sample. With one or more collection lenses containing the radiation
A phase controller configured to introduce two or more selected phase offsets into the illumination scattered by the sample, with a phase plate selector, one or more beam splitters, or at least one of the translational stages. Including phase control device and
A controller that is communicably coupled to the detector and includes one or more processors.
The one or more processors
Determining one or more scattering phase values introduced into an illumination beam scattered by one or more defects on the sample based on the two or more collected signals, and determining the one or more defects. Classification based on one or more of the scattering phase values according to a set of predetermined defect classifications.
A system configured to execute a program instruction configured to instruct the one or more processors. The phase plate selector is communicably coupled to the controller, and the phase plate selector inserts two or more phase plates sequentially into the radiation emitted from the sample to obtain the two or more selected phase offsets. Two or more collected signals configured to be introduced are sequentially generated by the detector in response to radiation emitted from the sample being modified by the two or more phase plates. The system according to claim 30, which corresponds to the above signals. The one or more beam splitters split the radiation emitted from the sample into two or more sample beams directed at the two or more phase plates to introduce the two or more selected phase offsets. Configured
The two or more collected signals are generated by the two or more detector assemblies of the detector in response to the correction of the radiation emitted from the sample by the two or more phase plates. The system according to claim 30, which corresponds to the above signals. The translational stage is configured to fix the sample, the translational stage is communicably coupled to the controller, and the translational stage has two of the sample along the optical axis of the one or more focusing lenses. It is configured to translate to the above focal positions to introduce the two or more different selected phase offsets, and the two or more collected signals are generated by the detector at the two or more focal positions. 30. The system of claim 30, which corresponds to two or more signals to be made. The set of predetermined defect classifications
30. The system of claim 30, comprising at least one of a metal, dielectric or organic material. The set of predetermined defect classifications
30. The system of claim 30, comprising at least one of silver, aluminum, gold, copper, iron, molybdenum, tungsten, germanium, silicon, silicon nitride and silicon dioxide. 30. The system of claim 30, wherein the illumination beam comprises an annular illumination beam. 36. The system of claim 36, wherein the illumination beam comprises a spatially coherent illumination beam. 36. The system of claim 36, wherein the illumination source comprises a narrowband illumination source. 38. The system of claim 38, wherein the illumination source comprises a speckle-removing laser source. 36. The system of claim 36, wherein the illumination source comprises a broadband illumination source. 40. The system of claim 40, wherein the broadband illumination source comprises an incoherent lamp source. 40. The system of claim 40, wherein the broadband illumination source comprises an adjustable broadband illumination source. 36. The system of claim 36, wherein the illumination beam comprises a spatially coherent illumination beam. 43. The system of claim 43, wherein the illumination beam comprises a laser source. 44. The system of claim 44, wherein the laser source comprises an adjustable laser source. In the pupil surface of the one or more collecting lenses, the system is further configured to suppress the illumination scattered by the surface of the sample with respect to the illumination scattered by the one or more defects on the sample. 30. The system of claim 30, further comprising a polarizer mask. 30. The system of claim 30, wherein the illumination beam comprises a single collimated illumination beam. 30. The system of claim 30, wherein the detector comprises a time delay integral (TDI) detector. 30. The system of claim 30, wherein the one or more focusing lenses and the one or more collecting lenses share at least one common element. It ’s a system,
A configuration phase the controller to introduce two or more selected phase offset illumination scattered by the sample, a phase plate selectors, one or more beam splitters, or the translation stage at least one Including phase control device and
With a controller that includes one or more processors,
The one or more processors
One or more scattering phase values introduced into an illumination beam scattered by one or more defects on the sample are determined based on two or more collected signals.
The one or more defects are classified based on the one or more defect phase values according to a set of predetermined defect classifications.
A system configured to execute a program instruction configured to instruct the one or more processors. Defect classification method
Illuminating the sample with an illumination beam and
Introducing two or more selected phase offsets into the illumination scattered by the sample, and
Collecting the illumination emitted from the sample to generate two or more collection signals corresponding to two or more selected phase offsets.
Determining one or more scattering phase values introduced into the illumination beam scattered by one or more defects on the sample based on the two or more collected signals.
It comprises classifying the one or more defects based on the one or more scattering phase values according to a predetermined set of defect classifications.
Defect classification method.

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